text: Some researchers study the occurrence of euxinia in ancient oceans because it was more prevalent then than it is today. Since ancient oceans cannot be directly observed, scientists use geology and chemistry to find evidence in sedimentary rock created under euxinic conditions. Some of these techniques come from studying modern examples of euxinia, while others are derived from geochemistry. Though modern euxinic environments have geochemical properties in common with ancient euxinic oceans, the physical processes causing euxinia most likely vary between the two.